For years, intelligent systems have promised to improve people's lives by inferring context and activities in diverse environments. In particular, people's interactions with objects offer rich, contextual information closely reflecting one's immediate environment and activity. Yet practical detection and recognition of object interactions has remained an elusive research goal. For example, although RFID systems can provide object recognition capabilities, the use of such systems requires all desired objects to be physically tagged with an RFID tag and, further, it is unknown if users are simply nearby or truly touching an object.
Electronic devices, especially those driven by motors (e.g., power drills) or switching power supplies (e.g., LCD screens), produce significant levels of electromagnetic noise. These unwanted signals propagate as radio frequency (RF) waves and can disrupt nearby devices operating with similar frequency bands. Beginning in the late 1970s, the US Federal Communications Commission (FCC) chartered mandates to regulate the susceptibility of consumer devices to EM noise. These were also established to prevent EM noise from interfering with other electronics, utilities, and purposeful broadcasts, such as TV and radio.
Infrastructures and environments also produce EM noise. For example, AC electricity and devices connected to power lines contribute to the majority of electrical noise at home. In general, EM noise propagates through conduction over circuits and power lines (1 kHz-30 MHz) or through radiation in free space (30 MHz to 10 GHz). Most EM noise sources in the home can be categorized as resistive (e.g., incandescent bulbs), inductive (e.g., brushed DC motors), or switching (generally solid state, e.g., most modern electronic devices).
Additionally, a few classes of non-electromechanical objects can have unique EM signatures. Most notable among these are large, conductive objects, such as structural members in buildings, doors, ladders, furniture, and window frame-work. These are sufficiently large that they act as antennas, capturing energy radiated by proximate noisy devices and wiring. The amalgamation of these signals, in our experiences, is fairly unique and particular to a location.
It is against this background that the techniques described herein have been developed.